June S, 1SS3.] 



SCIENCE. 



507 



beneath the cranium. It gives rise to the 

 lower part of the coclilea, the promontor}' and 

 lower part of the oval window, the round 

 window, the lower arm of the posterior semi- 

 circular canal, the lower part of the facial 

 canal, the jugular fossa, the carotid canal, and 

 the floor of the tympanum. 



The mastoid portion of the petrosal is pro- 

 duced, subsequent to the complete coalescence 

 of the prootic and opisthotic, by outgrowths 

 from the posterior and external semicircular 

 canals. Tlie outgrowth from the posterior 

 semicircular canal first shows itself externally 

 in the broad plate of cartilage which forms 

 part of the cranial wall between the squamosal, 

 the parietal, and occipital bones. It makes 

 its appearance as an elliptical islet just in ad- 

 vance of the occipital. In this condition it 

 has been viewed bj' Professor Huxley as a 

 distinct ossiflc centre, to which he has given 

 the name of the epiotic, regarding it as the 

 specialh- mastoid part of the mastoid portion 

 of the temporal bone. In m3' preparations, 

 the elliptical islet has appeared as a continuous 

 growth from the most prominent part, out- 

 wardly, of the posterior semicircular canal, 

 after the completion of this by the co-ossifica- 

 tioa of its arms, which spring separatelj- from 

 the prootic and opisthotic. Later, a second 

 element of the mastoid portion of the petrosal, 

 as an outgrowth of the external semicircular 

 canal, makes its appearance as a quadrate 

 islet in the cartilage intervening to the ellip- 

 tical islet and the squamosal. The two islets 

 quickh' unite, and thus together form the mas- 

 toid portion of the petrosal ; the notch between 

 them, above, still remaining at the upper ex- 

 tremity of the latter, at birth. From the ante- 

 rior or quadrate islet, the mastoid process is 

 subsequently developed, and not from the sup- 

 posed epiotic, as has been asserted. 



The squamosal and petrosal commonly- an- 

 chylose in the external portion of the petro- 

 squamosal suture, near the time of birth ; and 

 this portion of the suture is usually obliterated 

 during the first or second 3'ear subsequent!}-. 

 Sometimes traces of it remain as irregular 

 chinks, and rarel}' the greater extent or the 

 whole of it may be retained, as represented in 

 the accompanying fig. 3, from one of several 

 similar specimens in the university' museum. 

 The suture is observed to descend from the 

 notch at the upper border of the bone to the 

 point of the mastoid process ; and it thus indi- 

 cates that the anterior third of the mastoidea 

 pertains to the squamosal, while the rest alone 

 belongs to the petrosal. The internal portion 

 of the suture, commonlj- after some j-ears, is 



but partially obliterated, and frequentlj' re- 

 mains, to a variable extent, as a fissure defin- 

 ing the tegmen of the petrosal from- the inner 

 surface of the squamosal. 



The mastoid process, scarcelj- marked at 

 birth, becomes conspicuous onlj^ after a year 

 or two. The mastoid antrum is developed at 

 birth ; but the surrounding mastoid cellules 

 undergo but little development until after 

 pubert}'. ■ 



The external auditory meatus is produced 

 after birth. The 

 auditory plate 

 forming its roof 

 is graduallj' 

 more differenti- 

 ated from the 

 rest of the squa- 

 mosal, and its 

 tj'oipanic scute 

 becomes more 

 distinct bj^ the 

 production of 

 spong3' sub- Fig. 3.. 

 stance between 

 it and the roof 

 of the meatus. 

 The floor and 

 sides of the latter are produced from the tj'm- 

 panal ring, which becomes the tympanic plate 

 of the more mature bone. Lateral processes 

 grow outwardlj' from the ring, expand at the 

 ends, and conjoin to form the auditory pro- 

 cess, leaving an aperture in the tympanic plate. 

 The aperture is obliterated about the third or 

 fourth year, but occasionally is retained as an 

 imperfection, closed by fibrous membrane. 

 From growth downward and backward from 

 the tjTiipanal, the vaginal process and poste- 

 rior extremity of the t^^rapanic plate are pro- 

 duced. Joseph Leidy. 



oporal bone, one-balf size, 

 xhjbiting the outer pari of the petro- 

 pquaraosal suture, permanently re- 

 tained, and indicating the division of 

 the mastoidea into a squamosal and a 

 petrosal portion. 



THE NAPLES ZOOLOGICAL STATION.^ 

 II. 

 The fleet of boats belonging to the station, 

 to whose efficient services the constant supply 

 of material is due, consists of two steam- 

 launches and a number of row-boats and sail- 

 boats. The larger of the steamers, named, 

 after the great German biologist, ' Johannes 

 Miiller,' was given hy the Berlin academy of 

 sciences ; while the smaller, the ' Francis 

 Balfour,' was bought by the station. These 

 are used for long excursions, being absent in 

 summer sometimes for three or four days. 



^ Concluded from No. 17. 



